Apparatus for developing lithographic plates

ABSTRACT

Apparatus for postexposure treatment of lithographic plates having an endless belt on which such a plate is transported successively to, through, and beyond, a development station, a washing station, and a preserving station. The plate is rubbed at some of the treating stations by a rubbing device after having treating liquid deposited thereon. The plate undergoing treatment is held fast on the endless belt by interfacial tension.

[56] References Cited UNITED STATES PATENTS 2/1950 Luboshez...... 6/1951 2,677,320 /1954 Robert E. Harrell;

Arthur E. Essmueller; Roy C. Bax, all of St. Louis County, Mo.

United States Patent [72] Inventors plate is 49993 mmmmmof 555558 99999 5 9 2,555,874 Coughlin...

Coughlin...

3,059,560 10/1962 Gutzmer.... 3,088,391 5/1963 Sigler....... 3,271,226 9/1966 Staehleetal.

Primary Examiner-Samuel S. Matthews Assistant Examiner-Fred L. Braun [21] Appl. No.

[22] Filed May 14, 1968 Patented Sept. 28, 1971 [73] Assignee Western Litho Plate 8 Supply Co.

St. Louis, Mo.

Attorney-Koenig, Senniger, Powers and Leavitt ABSTRACT: Apparatus for postexposure treatment of lithographic plates having an endless belt on which such a transported successively to, through, and beyond, a development station, a washing station, and a preserving station. The plate is rubbed at some of the treating stations by a rubbing device after having treating liquid deposited thereon. The plate undergoing treatment is held fast on the endless belt by interfacial tension.

Int. G03d 5/00 95/89,94,

[54] APPARATUS FOR DEVELOPING LITHOGRAPHIC PLATES 10 Claims, 9 Drawing Figs.

[50] Field of Search.

PATENTED 8928 um SHEET 1 [IF 5 pAmun-insspzemn 3508.464

- SHEETEUFS FIGZ mimtn'ssrzenn 3.608.464

SHEET 3 [IF 5 PATENIEB swam SHEET k UF 5 Tut APPARATUS FOR DEVELOPING LITHOGRAPHIC PLATES The invention relates to apparatus for postexposure treatment of lithographicplates to press-ready condition by the additive process."

The additive process of lithographic plate treatment is applicable to both negative-working and positive-working plates. in the case of anegatively working plate, increments are added during the postexposure treatment to the light-reacted areas of the plate, whereas in the case of positively working plates, increments are added during the postexposure treatment to the nonlight-reacted areas of the plate. The additive process is to be distinguished from the subtractive process" wherein the postexposure treatment involves subtracting increments of nonlight-reacted areas in :the case of negatively working plates, and subtracting increments of light-reacted areas in the case of positive-working plates. In either process, however, the plate is provided on its active surface with a coating of material which reacts upon exposure to light, so as to change its wettability characteristic. The active surface of such a plate is usually exposed to light through a photographic transparencyhaving dark areas and clear areas. Upon exposure, the areas on the active surface of the plate which correspond in location to the clear areas are light struck (and,

hence become light-reacted), while all those areas on the plate which correspond to the dark areas of the transparency are nonlight-struck, and hence do not undergo light reaction.

Since in the additive process, comparable treatments produce comparable results on the light-reacted areas of a.

negative-working plate as on the nonlight-reacted areas of a positive-working plate, detailed descriptions of the former should suffice for the purpose of illustration.

The negative-working additive process necessitates that the light-struck areas on the active surface of the plate become organophilic and hydrophobic, while the nonlight-struck areas on the active surface of the plate remain hydrophilic and organophobic. The postexposure treatment of such plates, as heretofore carried out by hand, involves a series of steps. First,

a developer" emulsion or suspension is spread uniformly readily spreadable. The light-struck areas on the active surface of the plate have a preferential affinity for the organophile components of the developer, while the nonlight-struck areas of the plate have a preferential affinity for the hydrophilic components of the developer, are loosened and, at least to" some extent, washed away by the hydrophile components of the developer. ln development by hand, the time consumed in rubbing the developer on a large plate is usually sufficient to permit evaporation of enough of the organic vehicle to harden the lacquer, but in the case of small plates, such hardening is frequently expedited by fanning, with resultant vaporization of the organic vehicle.

The second step is to wash away, with water, all of the developer which is not adhered to the light-struck areas, and then to, at least partially, dry the active surface of the plate.

The third step in the hand operation is optional, but nonetheless the prevailing practice in the art. lt involves the application of a preservative to the hydrophile areas, and, in some cases, the application of a different preservative to the organophile areas of the plate. This increases the storage life of the plate prior to printing, and involves an operation manipulatively comparable to the first step, but with a less viscous emulsion or suspension which, for example, may contain an organophile grease and a water-soluble gum in a mixture of oil and water. Such components have preferential affinity, respectively, for the light-struck and the nonlight-struck areas of the plate. After appropriately spreading the composition and rubbing it until the plate is again dried at least to a substantial extent, the plate is ready for the press. 1

The three steps of the hand operation just described require an elapsed time of 10 minutes or more per plate, more time being required for large plates than for small ones.

One object of the invention is to expedite the postexposure treatment of lithographic plates.

Another object of the invention is to provide an apparatus for performing automatically the postexposure treatments of such plates, and to reduce the consumption of materials employed in such treatments.

These and other objects of the invention, which will become apparent to those skilled in the art as the description proceeds, are accomplished'by providing a machine having an endless belt for moving the exposed lithographic plate successively to, through and beyond, stations at each of which one of the steps of the above-described hand operation is performed, and preferably without interrupting the movement of the endless belt or moving the plate relative to the belt. The endless belt is preferably smooth enough and held flat enough that when a thin flexible sheet of' metal, such as a common lithographic plate, is laid upon it, air is excluded from the interface, and the two stick" together so long as the flat coincidence is maintained, an action which is facilitated if either contacting face is damp with a liquid which, at least to some extent, wets both. Accordingly, the belt is preferably made of a material which is, at least to some extent, phillic to liquids which are phillic to the reverse (nonactive) surface of the plate, and the belt is preferably of a material, for example neoprene, which may be vulcanized into endless condition in situ, i.e., while trained around one or more drive, or'guide, rollers forming a permanent part of the apparatus; and means is provided for assuring that the'belt is damp, but substantially devoid of unabsorbed or flowable liquid atthe time it receives a plate.

A salient feature of the invention is the provision of mechanism which both spreads the developer on a plate and rubs it. This is accomplished, in accordance with the present invention, by providing a continuously circulating pressurized system for supplying the developer liquid in metered quantities to a plate, and immediately thereafter to subject the plate to the action of a plurality of rubbing heads spaced apart a distance sufficient to enable at least part of the liquid components of the developer to evaporate from a given increment of the plates active surface before making contact with the succeeding head. Each head is equipped with a plurality of spaced rubbing members which are essentially porous, nonabrasive'and possessed of at least enough resiliency to compress, albeit slightly without permanent deformation. The rubbing members may have some, but preferably little, absorptivity toward the viscous developer. Any natural or synthetic sponge may be used as a rubbing member, but is is preferable that it be one whose average pore size is large, such as the so-called coarse-grain cellulose sponge of commerce. The coarse grain sponge is characterized by the fact that many of its pores are a quarter-inch or more in diameter, the average pore size being greater than three thirty-seconds of an inch with relatively few as small as one thirty-second inch, as distinguished from fine grain sponges whose pores are predominately on the order of one thirty-second inch in diameter, and, according to commercial practice, must be no greater than three thirty-seconds of an inch.

The spacing of the rubbing members on the leading rubbing head (i.e., the first rubbing head to make contact with a plate on the endless belt) is more important than to space them on the succeeding rubbing head. Such spacing of the rubbing members on the leading rubbing head is calculated to permit at least some of the developer deposited upon the plate, prior to reaching the leading rubbing head, to pass through the latter and be operated upon by the succeeding rubbing head. Consequently the invention contemplates that the developer be deposited upon a plate on the moving belt at a position ahead, and preferably immediately ahead, of the leading rubbing member. Preferably, the developer is deposited by dropping it in metered quantities from a plurality of outlets aligned in spaced relation transversely of the direction of movement of the plate.

In accordance with the present invention, the respective rubbing heads have their several rubbing members under slight, but substantially uniform, compression, e.g., enough to compress a coarse-grain cellulose sponge normally 1 inch thick to a thickness of about seven-eighths inch. While under such compression, and with an exposed lithographic plate moving thereunder, the respective rubbing members i are moved in a curvilinear orbit herein termed a doubly cranked link motion, which is the type of planar motion undergone by a link whose opposite ends are pivotally connected respectively to rotating cranks having the same throw. When such cranks are rotated in the same sense, every point on an interconnecting link revolves in a circular orbit whose center is fixed, and no two points in the same plane have the same orbit. On the other hand, when the two cranks of the link are revolved in opposite senses (and at least one crank is capable of small change in speed during a revolution), the orbit of the pivot axes at opposite ends is circular, but the orbit of the midpoint of the connecting link is oval. The doubly cranked link motion aforesaid eliminates the possibility that the paths of a given point on any one rubbing member will twice describe the same path on a plate moving rectilinearly therebeneath, and hence minimizes the likelihood of streaking.

After an increment of a plate moving with the endless belt has departed from the region of operation by the succeeding rubbing head, the active surface of the plate is subjected to a spray of water which erodes and washes from the plate passing therebeneath all of the loose material, solid and liquid, of the developer which has not, during the preceding treatments, become adhered to the light-reacted areas. Beyond the waterspray station, a wiping member of the squeegee type makes water-sealing engagement against the active surface of the plate. Such a squeegee may be either a roller or a blade, in either event having a contacting part of rubber, or other relatively soft material, which makes a substantially watertight seal with the plate traveling therebeneath. Thus unadsorbed and flowable water on the active surface of the plate is wiped off as the belt moves the plate under the squeegee, and such water is drained sidewise off the belt, as by tilting the belt at that region; and any tendency for such water to flow, counter to the belt movement, back into the developer station may be overcome by tilting the apparatus, or at least that region of the belt, so that gravity prevents such counterfiow.

Beyond the last-mentioned squeegee, the plate passes under another rubbing head, which may be of like character to the two previously mentioned, for rubbing the developer, but prior to passing under the third rubbing head, there is dropped upon the dewatered moving plate metered quantities of the preservative composition. As in the previous case, but with greater spacing transversely of the direction of movement of the plate, a series of spaced metering devices is arranged so as to drop the requisite quantity (usually less than that of the developer) of the preservative composition upon the subjacent plate. The preservative composition then undergoes rubbing of like character to that which the developer previously underwent. Upon emerging from the third rubbing head,

the plate is squeegeed to remove excess preservative (including entrained water and organic solvent). This completes the postexposure treatment in situations where the treated plates are transported individually from the apparatus to the press, as the time consumed in such transportation and in mounting the plates on the press is sufficient to permit natural evaporation of such water and organic solvent as may remain entrained in the residual preservative after the last-mentioned squeegeeing. On the other hand, where it is desired to accumulate plates emerging from the apparatus by stacking them one upon the other, it is advisable to expedite the evaporation of water and organic solvent as by passing the plates individually through any suitable dryer before they are stacked.

The series of postexposure treatment operations requires an elapsed time which is but a small fraction of that required when the operations are carried out by hand, and the drying aspect of the development operation, as well as that of the preservative application, is expedited by the air circulation induced by the doubly cranked link motion of the several rubbing heads.

FIG. 1 is an isometric view taken from a front or input corner of one embodiment of the apparatus, with portions of the covers and other parts broken away to reveal the relationship of working parts;

FIG. 2 is a plan view of the apparatus shown in FIG. 1 with the covers removed;

FIG. 3 is an end elevation of the apparatus shown in FIG. 1 with the covers removed,'some parts broken away, and taken from the front end, addressed toward the reader in FIG. 1;

FIG. 4 is a side elevation of the apparatus shown in FIGS. 1, 2 and 3, taken from the right side, addressed toward the reader in FIG. 1;

FIG. 5 is a partial sectional view taken along line 5+5 of FIG. 4, and showing the mechanism associated with one of the rubbing heads of said apparatus;

FIG. 6 is a bottom plan view showing the preferred arrangement of plate rubbing members on the pair of rubbing heads at the developer station of said apparatus;

FIG. 7 is a somewhat diagrammatic view showing the system for supplying developer to plates at the developer station;

FIG. 8 is a partial end view on enlarged scale and showing, in detail, a manner of securing a demountable rubbing assembly on a rubbing head; and

FIG. 9 is a somewhat diagrammatic view showing the system for supplying preservative composition to plates at the preservative station.

The apparatus shown in the drawings has an endless belt 1, the front loop of which is trained about an idler roller 2, and the rear loop of which is trained about a driven roller 3, so that the upper reach of the belt 1 moves from the roller 2 toward roller 3 to, through, and beyond, a superimposed front idler roll 4, a developing station 5, a washing station 6, a preservative station 7, and a rear squeegee roll 8, in succession.

The endless belt 1 is preferably made of neoprene, or other material which is flexible, substantially nonstretchable, and wettable by liquids which wet the reverse (inactive) surface of a lithographic plate to 'be' treated. Such wetting liquid is usually water, but, under certain circumstances, may be organophile, so it is preferred that the beltmaterial be, at least to a substantial extent, amphiphilic, which condition is satisfied by neoprene.

A lithographic plate 9 to be treated is fed into the apparatus across a feed apron 10 into the nip between front idler roll 4 and the upwardly addressed exterior surface of the upper reach of belt 1. From beneath idler roll 4, a platen 11, in the nature of a tabletop, extends continuously beneath the upper reach of belt 1 through stations 5, 6 and 7, and terminates just short of squeegee roll 8, thereby sustaining the upper reach of the belt in a substantially level or slightly sloping course, and providing a firm base for sustaining any vertical load imposed upon the upper reach of the belt as the plate 9 is transported on the belt 1 from the front end'of the apparatus to the rear end thereof.

DEVELOPING STATION At the developing station 5 of the embodiment shown, two spaced rubbing heads 12 and 13 are mounted for planar movement relative to, but parallel with, the plane of the upper reach of belt 1. In front of the leading rubbing head 12 there is affixed to a part of the stationary framework of the apparatus a series of metering devices 14, which periodically measure and drop charges of developer liquid upon the active surface of a lithographic plate, such as 9, traveling on the belt therebeneath. Optionally, for a purpose later to be described, some of the metering devices may be equipped with tubes 114 to lead their discharge onto the idler roll 4, or into the nip between that roll and an incoming plate.

An advantageous system for supplying developer liquid to the several metering devices 14 is shown in FIG. 7, and consists of a supply tank 141 connected to deliver liquid developer to the intake of a pump 142, which discharges through tube 143 to a header 144 to which the several metering devices 14 are connected. From the end of header 144 (remote from tube 143), a tube 145 extends back to tank 141.

*With such an arrangement, a stream of liquid developer is continuously moving under pressure through header 144 at all times during operation of the apparatus, and hence is available in well-agitatedcondition to supply developer liquid to all metering devices 14 simultaneously as demanded. Each of the metering devices has an electrically controlled valve which opens and closed in predetermined coordination with the movement of a plate therebeneath, or for preconditioning the cranked link motion, of the character above described, y

through mechanism later to be described in detail. The driving force is imparted by an. endless chain 15 which engages sprockets 16 and 17 on rubbing head 12, and sprockets 18 and 19 on rubbing head 13. In the form shown, all four sprockets are rotated clockwise, as seen in FIG. 2, but the general arrangement provides for numerous variations. For example, all sprockets may be rotated in the counterclockwise direction; the sprockets on one of the rubbing heads may be rotated in the clockwise direction, while the sprockets on the other rubbing head are rotated in the counterclockwise direction; the respective rubbing heads may be driven in phase (wherein the respective rubbing heads maintain the same spaced relationship between each other, and occupy no position which is not parallel with all other positions during a cycle), or out of phase (i.e., the respective rubbing heads occupy no position which is not parallel with every other position occupied during v a cycle, but the spaced relationship between the two does vary during a cycle). In fact, given freedom for slight lost motion at 7 one sprocket or the other, the respective sprockets on the same rubbing head may be rotated in opposite senses, a condition in which the given rubbing head occupies a multiplicity of positions in the course of a cycle which are not parallel with any other position, and the spacing from the companion rubbing head is constantly varying at opposite ends of the given rubbing head. Preferably, however, the rubbing heads 12 and 13 are driven as shown in the drawings, i.e., with all sprockets rotating in the same direction, but with rubbing head 13 moving 180 out of phase with the movement of rubbing head 12.

In the embodiment shown, each ofthe rubbing heads 12 and 13 is provided, at its lower extremity, with a platen 20 to the lower face of which there is detachably mounted an assembly of rubbing members. Such assembly preferably consists of a flat plate 21, to which there is appropriately secured, as by cementing, a series of seven rubbing members 22 each spaced from its neighbor, as shown in FIG. 6. The individual rubbing members are preferably a rectangular slab of coarse-grain cellulose sponge, or other comparable material, and the spaces between them preferably approximate half the amplitude of movement of the rubbing head in the horizontal direction which is at right angles to the movement of belt 1. Such spaced relationship of the individual rubbing members one from the other permits some increments of developer liquid deposited on a plate ahead of the leading rubbing head 12 to pass through the space between adjacent rubbing members on the leading rubbing head, and thus to be available at the trailing rubbing head 13. The spaced relationship of the rubbing members, coupled with the motion of the rubbing head, also induces turbulence in the circumambient air which expedites evaporation of the volatile components in the developer liquid being'rubbed. Angular orientation of the respective rubbing elements 22-relative to their supporting plate 21 is preferred,

and while such is not essential, excellent results are achieved when rectangular-shaped rubbing members are oriented on the plate 21 with one of their diagonals substantially parallel with the direction of movement of belt 1. The latter orientation minimizes the tendency of the leading increments of the respective rubbing members to bat increments of liquid developer, which they encounter in the course of their orbits, back toward the front of the apparatus. I

In the embodiment shown, the rubbing assembly 23 for the trailing rubbing head 13 is identical with that employed on the leading rubbing head 12, but with opposite slope. However, it should be pointed out that neither the spaced relationship nor the angular orientation of the rubbing members on the trailing rubbing head is of equal practical importance to those features on the leading rubbing head. In fact, a continuous slab of cellulose sponge, or equivalent material, having dimensions substantially corresponding with its supporting plate has some advantage over the spaced and angularly oriented arrangement shown in the drawings, but has the disadvantage that, in the field an attendant may inadvertently put the wrong rubbing assembly on the leading rubbing head. Such disadvantage assumes overriding importance because the rubbing members are expendable, and require frequent replacement.

The mechanism for moving the respective rubbing heads with the doubly cranked link motion aforesaid is shown in detail in FIG. 5, and is identical for each of the rubbing heads, as well, in the embodiment shown, as being identical at opposite ends of a given rubbing head. Such mechanism comprises a shaft 24 joumaled in a stationary part of the apparatus, and connected in rotational force-transmitting relationship with sprocket 16. At the lower end of shaft 24, a crank arm 25 is connected in rotational force-transmitting relationship. An eccentric stub shaft 26, projecting from crank arm 25, is journaledin a bearing 27 fixedly secured to rubbing head 12. The same organization of parts is provided for cooperation with sprocket 17. Consequently, upon rotation of the sprockets l6 and 17 in phase with each other, every individual point on rubbing head 12 revolves in a circular orbit about a center which is different from that about which any other point (in the same horizontal plane) in the rubbing head revolves. Preferably, the throw of crank 25 and its counterpart is substantially the same as the spacing between the respective rubbing members 22 on the leading rubbing head.

Since, in the preferred form, the several rubbing members 22 are resiliently compressible, and since greater pressure of the rubbing members is desirable on fine grained plates than on coarse-grained plates, means is provided for adjusting the degree of compression of the rubbing members and hence the pressure exerted by them upon a plate being operated upon. Such means is also shown in FIG. 5, and consists of a disc 28 fixed to a shaft 29, and secured for rotation within an annular cage 30 affixed to the upper side of platen 20. The shaft 29 is externally threaded to mate with internal threads on nut 31, which latter is affixed to the same part 32 of the rubbing head to which bearing 27 is affixed. At the upper end of shaft 29, there is a handwheel 33, or other manipulating device, whereby, upon turning shaft 29, the displacement between platen 20 and rubbing-head part 32 is varied. An identical arrangement is provided at the other end of the rubbing head, save that the counterpart of shaft 29 is foreshortened and provided with a sprocket 34 which is interconnected by a chain 35 with a sprocket 36 secured for rotation with shaft 29. Consequently, upon turning shaft 29, both ends of platen 20 are moved vertically relative to rubbing-head part 32 to the same extent, thereby to regulate the degree of compression in rubbing members 22, and the load imposed by them on a subjacent lithographic plate.

In order to facilitate the removal and replacement of the rubbing assemblieson the rubbing heads, the platens 20 of each rubbing head are provided with a pair of strips 37 extending along the opposite long sides thereof. Each of the strips 37 has a lip 38 which respectively extend toward each other in spaced relationship to the lower face of platen 20, as shown in FIG. 8. The spaced relationship approximates the thickness of rubbing assembly plate 21, so that a given plate 21 may be slid into and out of the raceway defined by the opposite lips 38. To secure the plates 21 in operative position, tag-shaped keepers 39 are connected eccentrically by bolts 40 to opposite ends of platen 20, so that when in the position shown in FIG. 8, with the bolts 40 run up tight, the keepers 39 prevent removal of plate 21, but when it is desired to remove the latter, one of the bolts 40 can be relaxed sufficiently to permit its associated tag-shaped keeper 39 to be rotated l80 out of the way of removing plate 21 by the sliding action above described.

The endless chain 15, which drives the several sprockets 16, 17, 18 and 19, is driven by a motor 41 in the conventional manner, and is engaged not only with the sprockets mentioned, but also with idler sprockets 42 appropriately positioned and equipped withb any suitable means for adjusting the axis of rotation of at least one of them, so as to properly regulate the tension on the endless chain. The endless chain also engages a pair of sprockets 43 and 44, which drive a comparable rubbing head 45 at the preservative station later to be described.

WASHING STATION Afer having been transported on the endless belt 1 under and beyond the rubbing heads 12 and 13, the leading edge of plate 9 emerges into washing station 6. A squeegee member 47 delineates the rear of the washing station, but one or more additional squeegee members, such as 48, may be provided if desired. Each of the squeegee members is equipped with a wiping blade, of resiliently flexible material such as rubber, or the like, which rides upon, and makes substantially water-sealing contact with, the subjacent increments of belt 1 or a lithographic plate thereon as the case may be. Such blade on the squeegee members 47 and 48 form dams to prevent the water released within the washing station from flowing to the rear past squeegee member 47.

Within the washing station, there is provided, in spaced relationship to the upper surface of belt 1, a water supply header 49 having a plurality of nozzles 50 from which there issues a shower of water directed toward the active surface of a subjacent plate, such as 9, as it passes therebeneath. The streams of water are so controlled and directed that substantially all increments of the active surface of the plate will be subjected to the rinsing and, to a minor extent, eroding action of the water streams, thereby to remove the hydrophile components of the developer liquid previously applied at the developing station, to the extent that the solids thereof are not already adhered to the already-hardened lacquer-forming components of the developer. The water released within the washing station is prevented from flowing back toward the developing station by tilting the entire apparatus, or at least the portion of platen 11 subjacent the washing station, in a direction such as to make it almost two degrees uphill from the squeegee 47 to the developing station. Water accumulated ahead of squeegees 47 and 48 flows sidewise of belt I, and if desired, the entire apparatus, or at least the portion of platen I1 beneath the washing station, may be tilted about 1 sidewise so that the water, squeegeed off, will flow by gravity over the opposite longitudinal edges of the belt and platen. If unlike the showing in the drawings, the tabletop platen 11, or a part thereof, has greater width than the belt 1, perforations may be provided in the portion of platen 11 which lies outboard of belt 1 so as to permit the escape of water therethrough, but in the embodiment shown, the squeegee members 47 and 48 extend for the full width of belt 1, the water released in the washing station flows over the edges of the belt, and is caught by a sink 51 disposed beneath the lower reach of belt 1. As the lithographic plate moves on the belt past squeegee members 47 and 48, the active surface thereof is substantially denuded of water by the squeegees.

PRESERVING STATION Upon emerging from the washing station 6, the lithographic plate, such as 9, passes under a proximity switch 52, which senses the presence of a subjacent plate on belt 1, and closes an electrical circuit whichactuates a plurality of metering devices 53, and results in the dropping of measured charges of preservative composition at predetermined intervals onto the active surface of a subjacent plate as it moves on belt I therebeneath into and through preserving station 7. As shown in FIG. 9, the several metering devices 53 are connected at spaced intervals of about five to six inches in the widthwise direction (of the belt) to a header 54, which is fixedly mounted upon the framework of the apparatus, and connected through tube 55 to a pump 56 which receives the preservative composition from tank 57. This organization is such that the preservative composition is under constant pressure and continuous flow in header 54, but tank 57 is vented to prevent the pump 56 from drawing a vacuum. While the tank 57 is shown with an open top, it will be understood that a lid may be applied to reduce evaporation of volatile components of the developer. A drain line 58, having a valve 59, is provided for draining the contents of tank 57 when operation of the apparatus is to be discontinued for a substantial period of time.

Also included within the preserving station 7 is the rubbing head 45 previously mentioned, whose construction and mode of operation is, in the embodiment shown, identical with that of developer rubbing head 12, except that where a single rubbing head is provided as at the preserving station, it is preferred that the shafts thereof, corresponding to 24 in FIG. 5, be provided at their upper ends with counterweights 61, or other balancing means, to minimize vibration, which balancing means is not necessary with rubbing heads 12 and 13 when driven in the same sense of rotation, but out of phase, as previously described. The counterweights 61 are mounted on the upper extremities of shafts corresponding to 24 in FIG. 5, and so oriented that the mass centers of the respective counterweights are in 180 displacement from the pivot axis of bearing 27 about stub shaft 26. Hence, the rubbing head 45 performs the same type of operation on an subjacent plate with preservative composition, as rubbing heads 12 and 13 performed at the developing station with developing composition, and rubbing head 45 is driven by the endless chain 15 in engagement with sprockets 43 and 44 in like manner to that previously described.

Upon emerging from the rubbing head 45, a lithographic plate, such as 9, is transported on the belt 1 into the nip between the belt 1 and a squeegee roller 8 which squeegees off any excess of preservative composition on the active surface of the plate, and accumulates it ahead of the nip between the belt and idler roll 8, so that it may drain sidewise of the belt and flow into sink 57, as in the case of the water discharged at the washing station 6.

When a lithographic plate, such as 9, emerges from between the roller 8 and belt 1, it is, under most conditions prevailing in the industry, ready for the press, but, depending upon ambient atmospheric conditions prevailing and the mode of handling in a given plant, it may be desirable to provide a heater and/or fanning means beyond roller 8, particularly if the plates undergoing treatment in the apparatus are stacked one upon the other immediately as they emerge from the squeegee 8. Accordingly, where such stacking is practiced, any suitable device, such as an oven, for expediting the natural evaporation of water and organic solvent from the preservative on the plate is recommended. Such an oven or other drying device is preferably arranged to receive the plates, one by one, as they emerge from squeegee 8, dry them, and automatically deliver them to a stacking device from which they may be removed at will in multiple.

ENVIRONMENT AND CONDITIONING In order to assure not only that the belt 1 is damp to the extent sufficient to exclude air from the interface between the exterior surface of the belt which comes into contact with the inactive (reverse) surface of an incoming plate at'the front loop of belt 1, but also to remove from the belt, before it comes into such contact with the plate, substantially all liquid which is neither absorbed nor adsorbed by the belt, the invention further contemplates that the lower reach of the belt be sprayed with water as it passes above sink 51, andthat" the unadsorbed or flowable water on the belt be removed therefrom as it turns at the front loop thereof about idler roll 2. This is accomplished by the provision of a water-spray head 62, whose nozzle is addressed toward the exterior surface of the lower reach of the belt, and by the provision of a squeegee 63 having a blade 64, of material such as rubber, in wiping contact with the exterior surface of belt 1 adjacent roller 2.

Thus, both spray head 62 and squeegee 63 are arranged so that the drainage therefrom is accumulated in sink 51. The residual water on an increment of belt 1 which has just passed squeegee 63 is substantially all adsorbed by the belt so that the belt is damp when the reserve (inactive) surface of an incoming plate, such as 9, first makes contact with the belt. Such dampness is enough to exclude air from the.plate-belt interface when the two are squeezed together bythe idler roll 4, and the resultant interfacial tension holds the plate in position on the belt, without relative movement, while the active (obverse) surface of the plate is undergoing the rubbing action of the heads 12, 13 and 45, and undergoing the wiping action of squeegees 47 and 48.

In some localities, the water supply, while potable, contains solutes which have a deleterious efiect when such water is brought into contact with the active face of an un-.

derdeveloped, but exposed, lithographic plate. In such circumstances, some precaution should be taken to prevent the unsatisfactory water transferred from the .belt 1 to idler roll 4 from being retransferred to the active surface of an incoming plate when the latter passes under the roll 4. Such problem is adequately overcome by running the roll 4 wet with developer composition. Hence, as shown in the drawing, three of the developer-metering devices 14 are equipped with tubes 114 which direct their discharge either onto roll 4 or into the nip between it and belt 1 (or an incoming plate on belt 1). Another solution is to dampen the belt 1 with a liquid, other than water, which is phillic toward both the exterior surface of belt 1 and the reverse face of a lithographic plate. The usual developer liquids of commerce suffice for this purpose.

The input apron 10 is equipped with means for sensing the presence, on the apron, of an incoming exposed lithographic plate, such as 9. In the form shown in the drawings, such a plate-presence sensor is in the form ofa whisker switch 65, which normally projects above the level of plate 10, but is pressed down into electrical-oircuit-closing position when an incoming plate engages it.

ln normal operation, the apparatus is started manually to precondition it for operation, a few seconds before a plate, such as 9, is inserted. At such startup, after the apparatus has been idle for a considerable period, the several components of the apparatus are actuated in sequence. First, the pumps 142 and 56 are energized to build up a head of developer composition in the developer header 144, and a head of preservative composition in header 54. Secondly, the movement of belt 1 is initiated simultaneously with turning on the water to headers 49 and 62. After the belt has moved at least for the distance between water header 62 and rubbing head 12, the several metering devices 14, which control the discharge of developer liquid, are opened to deposit on the belt a sufficient amount of developer liquid to impregnate at least the surface increments of the several rubbing members 22 on the developer heads 12 and 13. At the same time, and without regard to the control by proximity switch 52, the metering devices 53 are opened to deposit a charge of preservative composition on the belt for .LLL

the purpose of impregnating at least the surface increments of the rubbing members on preservative head 45. This actuation of the several metering devices is brief, for example, one or two squirts from each metering device, whereupon the electrical circuits which control the metering devices during the preconditioning stage are deenergized, and control of the metering devices is taken over by the whisker switch 65 and the proximity switch 52, respectively. Concurrently with the first preconditioning discharge from the several metering devices, motion of the several rubbing devices 12, 13 and 45 is initiated and continued for as long as desired, without actuation of the whisker switch by an incoming plate, but if, during this period, an incoming plate does actuate the whisker switch 65, the movement of the rubbing heads, as well as belt 1 continues without interruption. If desired, however, the electrical control circuitry may be automated to interrupt the continued movement of the belt and'rubbing head upon either the lapse of a chosen increment of time, or belt travel for a chosen distance, since the last actuation of the whisker switch.

In the continuous operation following preconditioning, the belt 1 and all rubbing members continue to move; and once the whisker switch 65 is actuated, the metering devices 14 will be automatically energized to deliver a charge from each of the metering devices, and to drop that chargeupon the subjacent plate near the leading edge thereof, as well as to auto matically drop succeeding charges on the plate every four or six inches. Likewise, whenever the proximity switch 52-senses the presence of a plate beneath it, the control circuitry for metering devices 53is-energized to cause periodic discharge of preservative after the plate has reached aposition to intercept the dropping discharges; The electrical circuitry and equipment for so controlling the metering devices 14 can take any form well known in the art, and forms no part of the present invention. The time at which movement of the rubbing heads l2, l3 and 45 is initiated is not critical, save that such initiation of each such rubbing head should occur prior to the time the leading edge of an approaching plate reaches it. The discharge of water from nozzles 50 may be continuous once motion of the belt 1 has been initiated, but, if desired, means for sensing the approach of a plate can be provided to turn the water discharge on when there is need for it, and off when there is no need for it. As pointed out hereinbefore, the discharge of preservative composition from metering devices 53 is under the control of proximity switch 52, so that discharge of preservative liquid commences after the leading edge of a plate undergoing processing has reached a position below the metering devices 53, continues periodically as long as a plate is present beneath proximity switch 52, and is terminated when there is no plate beneath proximity switch 52. The frequency of the discharges from metering devices 14 and 53 depend, to some extent, upon the developer and preservative compositions employed, as well as the character of the plate being treatedand its area. Accordingly, it is contemplated that the timing of such discharges be adjustable to best suit the prevailing conditions of operation, but the specific means for accomplishing such variation are well known in a variety of forms for-comparable situations, and form no part of the present invention.

While one complete embodiment of the invention has been described in detail, his not to be understood that the invention is limited to the embodiment so disclosed. On the contrary, it is realized that numerous modifications and variations will occur to those skilled in the art without departing from the spirit of the invention or the scope of the appended claims.

Having thus described the invention, what is claimed and desired to be secured by Letters Patent is:

1. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, a lithographic-plate-receiving station adjacent one end of said reach, said upper reach supporting and transporting a received plate to, through and beyond a succession of operating stations located along said reach, said belt having an exterior surfacefacing upwardly in said upper reach, means for applying liquid to said exterior surface, and means engaging said exterior surface ahead of said plate receiving station for removing substantially all but absorbed and adsorbed liquid from successive increments of said exterior surface, and wherein one of said operating stations has:'

a. means above said upper reach for measuring charges of developer liquid and dropping them upon a subjacent lithographic plate transported on said upper reach;

b. 'a rubbing head having a resiliently compressible porous rubbing member arranged to engage a lithographic plate moving on said belt beneath said head; and

c. means simultaneously, compressing said rubbing member and impartingpluridirectional rhotionthereto} 2. Apparatus for developing lithographic platescomprising a moving endless belt having a substantially horizontal upper reach, a lithographic-plate-receiving station adjacent one end of said reach,*said upper reach supportingandtransporting a" received plate to, through and beyond a succession of operating stations located along said reach, said belt having an exterior surface facing upwardly in said upper reach, means for applying liquid to said exterior surface, and means engaging said exterior surface ahead of said plate receiving station for removing substantially all but absorbed and adsorbed liquid from successive increments of said exterior surface, and wherein one of said operating stations has:

a. means above said upper reach for measuring charges of developer liquid and dropping them upon a subjacent lithographic plate being transported on said upper reach;

b. means for supplying said measuring means with developer liquid; and

c. means for maintaining continuous circulation of developer liquid through said means for supplying said measuring means with developer liquid.

3. Apparatus for processing exposed lithographic plates comprising:

means for continuously conveying an exposed plate along a predetermined path with the exposed sensitized face of the plate facing up;

means at a first location along said path for applying a developer for the plate on to the upper face of the plate, with the developer distributed across the upper face of the plate;

means at a second location along said path movable relative to the plate-conveying means for rubbing the developer over the upper face of the plate;

means at a third location along said path for spraying water on the upper face ofthe plate to wash off excess developer therefrom;

means at a fourth location along said path for wiping off water from the upper face of the plate;

means at a-fifth location along said path for applying a' preservative to the upper face of the plate, with the preservative distributed across the upper face of the plate; and

means at a sixth location along .said path for rubbing the preservative over the upper face of the plate.

4. Apparatus as set forth in claim 3 wherein the rubbing means at the said'second location is movable to rubin th developerlaterallyandlongitudinally'ofsaidpath.

5. Apparatusas set forth in claim 4 wherein the rubbing. means at the said second location comprises resiliently compressible means engageable with the upper face of a pate, and

1 having means for adjusting ithessaid rubbing .means at the said with the upper face of a plate, and having means for adjusting each rubbing means up and down relative to the plate-conveying means for varying the pressure of the rubbing means on the plate.

8. Apparatus as set forth in claim 3 wherein the plate-conveying means comprises an endless belt having an upper reach for conveying a plate along said path, the plate being applied to the upper reach of the belt adjacent one end thereof constituting its starting end, and having means for wetting the belt ahead of said one end of its upper reach for holding a plate flat on the belt.

9. Apparatus as set forth in claim 8 wherein at least that portion of the said upper reach of the belt from the third to the fourth location is inclined slightly downward.

10. Apparatus as set forth in claim 8 wherein the belt has a lower return reach and the belt-wetting means comprises means for spraying water on the bottom surface of the lower reach of the belt, and means for wiping off excess water from the lower reach. 

1. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, a lithographic-plate-receiving station adjacent one end of said reach, said upper reach supporting and transporting a received plate to, through and beyond a succession of operating stations located along said reach, said belt having an exterior surface facing upwardly in said upper reach, means for applying liquid to said exterior surface, and means engaging said exterior surface ahead of said plate receiving station for removing substantially all but absorbed and adsorbed liquid from successive increments of said exterior surface, and wherein one of said operating stations has: a. means above said upper reach for measuring charges of developer liquid and dropping them upon a subjacent lithographic plate transported on said upper reach; b. a rubbing head having a resiliently compressible porous rubbing member arranged to engage a lithographic plate moving on said belt beneath said head; and c. means simultaneously compressing said rubbing member and imparting pluridirectional motion thereto.
 2. Apparatus for developing lithographic plates comprising a moving endless belt having a substantially horizontal upper reach, a lithographic-plate-receiving station adjacent one end of said reach, said upper reach supporting and transporting a received plate to, through and beyond a succession of operating stations located along said reach, said belt having an exterior surface facing upwardly in said upper reach, means for applying liquid to said exterior surface, and means engaging said exterior surface ahead of said plate receiving station for removing substantially all but absorbed and adsorbed liquid from successive increments of said exterior surface, and wherein one of said operating stations has: a. means above said upper reach for measuring charges of developer liquid and dropping them upon a subjacent lithographic plate being transported on said upper reach; b. means for supplying said measuring means with developer liquid; and c. means for maintaining continuous circulation of developer liquid through said means for supplying said measuring means with developer liquid.
 3. Apparatus for processing exposed lithographic plates comprising: means for continuously conveying an exposed plate along a predetermined path with the exposed sensitized face of the plate facing up; means at a first location along said path for applying a developer for the plate on to the upper face of the plate, with the developer distributed across the upper face of the plate; means at a second location along said path movable relative to the plate-conveying means for rubbing the developer over the upper face of the plate; means at a third location along said path for spraying water on the upper face of the plate to wash off excess developer therefrom; means at a fourth location along said path for wiping off water from the upper face of the plate; means at a fifth location along said path for applying a preservative to the upper face of the plate, with the preservative distributed across the upper face of the plate; and means at a sixth location along said path for rubbing the preservative over the upper face of the plate.
 4. Apparatus as set forth in claim 3 wherein the rubbing means at the said second location is movable to rub in the developer laterally and longitudinally of said path.
 5. Apparatus as set forth in claim 4 wherein the rubbing means at the said second location comprises resiliently compressible means engageable with the upper face of a plate, and having means for adjusting the said rubbing means at the said second location up and down relative to the plate-conveying means for varying the pressure of the rubbing means on the plate.
 6. Apparatus as set forth in claim 3 wherein the rubbing means at the second location and the rubbing means at the sixth location are both movable to rub laterally and longitudinally of said path.
 7. Apparatus as set forth in claim 6 wherein each rubbing means comprises resiliently compressible means engageable with the upper face of a plate, and having means for adjusting each rubbing means up and down relative to the plate-conveying means for varying the pressure of the rubbing means on the plate.
 8. Apparatus as set forth in claim 3 wherein the plate-conveying means comprises an endless belt having an upper reach for conveying a plate along Said path, the plate being applied to the upper reach of the belt adjacent one end thereof constituting its starting end, and having means for wetting the belt ahead of said one end of its upper reach for holding a plate flat on the belt.
 9. Apparatus as set forth in claim 8 wherein at least that portion of the said upper reach of the belt from the third to the fourth location is inclined slightly downward.
 10. Apparatus as set forth in claim 8 wherein the belt has a lower return reach and the belt-wetting means comprises means for spraying water on the bottom surface of the lower reach of the belt, and means for wiping off excess water from the lower reach. 